The present invention is directed to an electrophoresis plate, and more particularly to an electrophoresis plate which is packaged with a plastic film on it.
Valuable information can be obtained by an analysis of certain biological fluids from a patient, such as blood serum, when diagnosing the patient's illness. Electrophoresis is known to be an effective technique for separating the various components of such fluid for subsequent analyses using optical densitometry techniques. The physical phenomenon underlying electrophoretic analysis is that particles which have an effective electric charge and which are deposited on a solid or semi-solid medium are caused to move with respect to the medium by an electric field applied across the medium. Particles of different types move at different rates, so a mixture of different types of particles is separated into its different components or fractions by electrophoretic analyses. These separated fractions may then be stained (visualized) by exposing them to a suitable reagent so that the fractions can be optically detected using visible or ultraviolet light.
The electrophoresis process has been performed through a series of manual steps for many years. The manual process typically has started with the operator preparing an electrophoresis chamber by filling appropriate cavities of the chamber with buffer solution. Buffer solution is a liquid used in the electrophoresis process to provide an electrical interface to a power source so that an electric field may be applied to the medium and to contribute to maintaining the surface of the electrophoresis medium in a moist condition. The electrophoresis medium is typically a gel substance such as agarose that has been fixed onto a suitable substrate (e.g., Mylar) to form an electrophoresis plate. The liquid sample to be examined is typically blood serum, but of course may be other liquids.
After the operator has prepared the electrophoresis chamber, he then applies appropriate sample volumes to precise locations on the electrophoresis medium. The operator then places the medium into the electrophoresis chamber so that the edges of the medium are immersed in two buffer cavities at each of its longitudinal ends. Electrophoresis is then performed using a precise and consistent voltage differential applied for a precise and consistent interval of time across the buffer cavities and therefore the complete surface.
After electrophoresis has been completed, the operator applies a uniform coating of a development reagent to the surface of the medium, allowing a precise and consistent interval of time for the reagent and sample to chemically . react. The development reagent is a liquid used after electrophoresis to chemically react with the separated fractions of the fluid sample, causing the fractions to exhibit optical characteristics.
Next, the operator places the electrophoresis medium into a temperature-controlled oven and incubates it using a precise and consistent temperature and time interval. Incubation is the process of controlling the chemical reaction between the fractions of the liquid sample and the development reagent by means of applying heat for a fixed interval of time.
Next, the operator dries the electrophoresis medium by increasing the oven temperature for a second precise and consistent temperature and time interval. The drying process stops the reaction between the separated fractions and the reagent by removing water from the medium. The medium can then be examined using optical densitometry techniques to determine which fractions were present in the original samples and to find their relative proportions.
The manual process described above requires careful attention by the operator in order to provide accurate and reproducible results. It is therefore not surprising that techniques for performing electrophoresis automatically have been developed. For example, U.S. Pat. Nos. 4,360,418 and 4,391,689 to Golias describe an automated electrophoresis and staining apparatus and method. U.S. Pat. Nos. 4,810,348, 4,890,247, 4,909,920, and 4,954,237 to Sarrine et al also describe an automated electrophoresis apparatus and method. An automated applicator assembly with pipettes for transferring samples to the electrophoresis medium during automatic analysis is described in U.S. Pat. Nos. 4,827,780 and 4,938,080 to Sarrine et al. All of these patents, which are assigned to the assignee of the present invention, are incorporated herein by reference.
Electrophoresis plates for use with automatic equipment are typically distributed with plastic films over the working portion of the electrophoresis medium layer. The film protects the working portion from contaminants and also prevents evaporation of water and thus helps to maintain the. integrity of the electrophoresis medium layer during storage. This film must be removed by the operator before the fluid samples are deposited on the electrophoresis medium layer.
The electrophoresis plate is typically made by placing a substrate in a mold and injecting a thermosetting gel. The gel has a liquid component which includes water, a buffer, and frequency additional substances. For example, in the past surfactants such as tritons have been included in the liquid to produce better separation of the samples and to improve resolution and stability. The protective film is applied to the electrophoresis medium layer after the completed electrophoresis plate has been removed from the mold, and soon thereafter the electrophoresis medium layer begins to expel or express a small portion of the liquid in the gel due to a phenomenon known as syneresis. The expressed liquid accumulates in a layer between the surface of the electrophoresis medium layer and the protective film and is retained there by capillary action.
When the operator of the automatic electrophoresis equipment removes the protective film, the accumulated liquid forms thin, irregular patches or pools on the surface of the electrophoresis medium layer. Since the liquid is electrically conductive these irregular patches provide irregular current paths and thereby keep the electrophoresis medium layer from being electrically homogeneous at its upper surface. For this reason it has been customary for the operator to remove the accumulated liquid by blowing it away, for example, or by blotting the electrophoresis plate against an absorbent surface.
Removal of the accumulated liquid by the operator increases the risk that the electrophoresis medium layer might become contaminated or that its integrity/uniformity might become compromised. Contamination by lint is a particular problem, since lint may carry brighteners which fluoresce under ultraviolet light and since automatic electrophoresis equipment typically employs ultraviolet light when reflectance densitometric techniques are used to read the separated proteins on the electrophoresis plate.